Make sure your Known Traveler Number (KTN) is preserved in your profile by logging into your MileagePlus account before adding TSA PreCheck to your United Airlines reservation. If not, fill up the Profile and Preferences box with your KTN. To add your KTN to an existing reservation, visit United\s \Manage Reservations\ page, How Do You Add TSA PreCheck to United Airlines <br> pick the booking, and then click Edit Traveler Information. Additionally, you can give your KTN to a United representative in person at the airport or when checking in online. If you qualify, TSA PreCheck will appear on your boarding pass after it has been added.